Steganographic Encoding

ABSTRACT

The present invention relates generally to steganographic encoding. Once claim recites a method including: obtaining plural-bit auxiliary data; creating an original carrier signal representing the plural-bit auxiliary data; reducing information content of the original carrier signal so that the carrier still conveys the plural-bit auxiliary data, yielding a reduced carrier signal; and hiding the reduced carrier signal in host data. Another claim recites a mechanical part including: a metallic surface including a pattern, the pattern conveying plural-bit auxiliary data in a steganographic manner, and the pattern provides at least diffuse reflection. Of course, other claims and combinations are also provided.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.11/621,459, filed Jan. 9, 2007 (now U.S. Pat. No. 7,403,633) which is acontinuation of U.S. patent application Ser. No. 10/359,550, filed Feb.5, 2003 (now U.S. Pat. No. 7,162,052), which is a continuation-in-partof U.S. patent application Ser. No. 10/286,357, filed Oct. 31, 2002 (nowU.S. Pat. No. 7,065,228). The 10/359,550 application is also acontinuation of U.S. patent application Ser. No. 10/165,751, filed Jun.6, 2002 (now U.S. Pat. No. 6,754,377), which is a continuation of U.S.patent application Ser. No. 09/074,034, filed May 6, 1998 (now U.S. Pat.No. 6,449,377). The 09/074,034 application claims the benefit of U.S.Provisional Patent Application No. 60/082,228, filed Apr. 16, 1998. Eachof these U.S. Patent documents is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to methods and systems forsteganographically arranging data on specular surfaces (e.g.,mirror-like surfaces) and associated methods/systems for decodingsteganographically-arranged data from such surfaces.

BACKGROUND AND SUMMARY OF THE INVENTION

Counterfeiting and forgeries continue to proliferate. A hot area ofcounterfeiting is consumer products, such as cellular phones, logos andcameras. Often cellular phones include interchangeable faceplates. (Or acamera includes a logo plate, which is easily replicated by thieves.). Acommon counterfeiting scenario involves counterfeiting the faceplate,and then passing off the counterfeit faceplate as genuine.

One solution is to provide steganographic auxiliary data in or onconsumer products to help prevent or detect counterfeiting. The data canbe decoded to determine whether the object is authentic. The auxiliarydata may also provide a link to a network resource, such as a web siteor data repository. The absence of expected auxiliary data may alsoprovide a clue regarding counterfeiting.

One form of steganography includes digital watermarking. Digitalwatermarking systems typically have two primary components: an encoderthat embeds the watermark in a host media signal, and a decoder (orreader) that detects and reads the embedded watermark from a signalsuspected of containing a watermark. The encoder can embed a watermarkby altering the host media signal. The decoding component analyzes asuspect signal to detect whether a watermark is present. In applicationswhere the watermark encodes information, the decoder extracts thisinformation from the detected watermark. Data can be communicated to adecoder, e.g., from an optical sensor.

One challenge to the developers of watermark embedding and readingsystems is to ensure that the watermark is detectable even if thewatermarked media content is transformed in some fashion. The watermarkmay be corrupted intentionally, so as to bypass its copy protection oranti-counterfeiting functions, or unintentionally through varioustransformations (e.g., scaling, rotation, translation, etc.) that resultfrom routine manipulation of the content. In the case of watermarkedimages, such manipulation of the image may distort the watermark patternembedded in the image.

A watermark can have multiple components, each having differentattributes. To name a few, these attributes include function, signalintensity, transform domain of watermark definition (e.g., temporal,spatial, frequency, etc.), location or orientation in host signal,redundancy, level of security (e.g., encrypted or scrambled), etc. Thecomponents of the watermark may perform the same or different functions.For example, one component may carry a message, while another componentmay serve to identify the location or orientation of the watermark.Moreover, different messages may be encoded in different temporal orspatial portions of the host signal, such as different locations in animage or different time frames of audio or video. In some cases, thecomponents are provided through separate watermarks.

There are a variety of alternative embodiments of an embedder anddetector. One embodiment of an embedder performs error correction codingof a binary message, and then combines the binary message with a carriersignal to create a component of a watermark signal. It then combines thewatermark signal with a host signal. To facilitate detection, it mayalso add a detection component to form a composite watermark signalhaving a message and detection component. The message component includesknown or signature bits to facilitate detection, and thus, serves a dualfunction of identifying the mark and conveying a message. The detectioncomponent is designed to identify the orientation of the watermark inthe combined signal, but may carry an information signal as well. Forexample, the signal values at selected locations in the detectioncomponent can be altered to encode a message.

One embodiment of a detector estimates an initial orientation of awatermark signal in a host signal, and refines the initial orientationto compute a refined orientation. As part of the process of refining theorientation, this detector may compute at least one orientationparameter that increases correlation between the watermark signal andthe host signal when the watermark or host signal is adjusted with therefined orientation.

Another detector embodiment computes orientation parameter candidates ofa watermark signal in different portions of a signal suspected ofincluding a digital watermark, and compares the similarity oforientation parameter candidates from the different portions. Based onthis comparison, it determines which candidates are more likely tocorrespond to a valid watermark signal.

Yet another detector embodiment estimates orientation of the watermarkin a signal suspected of having a watermark. The detector then uses theorientation to extract a measure of the watermark in the suspectedsignal. It uses the measure of the watermark to assess merits of theestimated orientation. In one implementation, the measure of thewatermark is the extent to which message bits read from the targetsignal match with expected bits. Another measure is the extent to whichvalues of the target signal are consistent with the watermark signal.The measure of the watermark signal provides information about themerits of a given orientation that can be used to find a better estimateof the orientation. Of course other watermark embedder and detectors canbe suitably interchanged with some embedding/detecting aspects of thepresent invention.

Some techniques for embedding and detecting watermarks in media signalsare detailed in the assignee's co-pending U.S. patent application Ser.No. 09/503,881, U.S. Pat. No. 6,122,403 and PCT patent applicationPCT/U.S. Pat. No. 02/20832 (published as WO 03/005291), which are eachherein incorporated by reference. The artisan is assumed to be familiarwith the foregoing prior art.

In the following disclosure it should be understood that references towatermarking and steganographic hiding encompass not only the assignee'stechnology, but can likewise be practiced with other technologies aswell.

Recent developments of highly reflective films and surfaces haverequired consideration of how best to steganographically mark thesetypes of surfaces. One such surface is a so-called specular surface. Aspecular surface often reflects light away from the light's source. Thiscan create signal detection problems since relevant optical scan datamay be reflected away from a co-located optical sensor.

Accordingly, one aspect of the present invention provides a method ofsteganographically marking a specular surface. The method includes stepsto provide a steganographic signal including at least plural-bit data,and to arrange ink in a pattern on the specular surface to represent thesteganographic signal. The ink, once arranged on the specular surface,provides a surface including at least a diffuse reflection property.

Another aspect of the present invention provides a method of marking aspecular surface. The method includes the steps of: providing an imageincluding generally uniform pixel values; embedding a digital watermarksignal in the image, which effects a change to at least some of thegenerally uniform pixel values; thresholding the digitally watermarkedimage; and printing the thresholded, digitally watermarked image on thespecular surface with an ink or dye that, once printed, provides an inkor dye surface comprising at least a diffuse reflection property.

Yet another aspect of the present invention is a three-dimensionalmolded article. The article includes a decorative film or substrate andan adjacent molded polymeric base. The decorative film or substrateincludes a specular surface. An improvement to the article is asteganographic signal applied to the decorative film or substratethrough arranging an ink pattern on the specular surface. A colorationof the ink is selected to conceal the ink pattern on the specularsurface.

Still another aspect of the present invention is a method ofsteganographically marking a mirror-like surface. The mirror-likesurface includes a first coloration and a first finish. The methodincludes the steps of providing a steganographic signal including atleast plural-bit data, and arranging ink in a pattern on the mirror-likesurface to represent the steganographic signal. The ink forms a surfacewhich provides Lambertian reflection. At least one of an ink colorationand ink finish is selected to hide the ink with respect to at least oneof the first coloration and the first finish.

Yet another aspect of the present invention is a laminate comprising amulti-layered structure including a film having a specular surface. Thefilm is sandwiched between a polymeric substrate and an over-laminate.An improvement to the laminate is ink adjacently arranged to thespecular surface so as to convey a steganographic signal. The inkprovides an ink surface with a diffuse reflection property.

The foregoing and other features and advantages of the present inventionwill be even more readily apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings.Of course, the drawings are not necessarily presented to scale, butrather focus on inventive aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates changes to the width of a line to effect watermarkencoding. FIG. 1 corresponds to FIG. 5 in parent U.S. Pat. No.6,449,377.

FIG. 2 illustrates a reflectance example for a specular surface.

FIG. 3 illustrates the specular surface of FIG. 2 including asteganographic signal conveyed through arrangement of ink or dye.

FIG. 4 a illustrates a reflectance example for a preferred ink or dyethat conveys a steganographic signal.

FIG. 4 b illustrates a reflectance example including an optical sensorremotely located with respect to a light source.

FIG. 5 a illustrates a flow diagram for a signal hiding method accordingto one aspect of the present invention.

FIG. 5 b illustrates a flow diagram for the FIG. 5 a method including athresholding step.

FIG. 6 illustrates a cross-sectional view of a multi-layered discaccording to one embodiment of the present invention.

DETAILED DESCRIPTION

In parent U.S. Pat. No. 6,449,377 we teach:

In a first embodiment of the invention, shown in FIG. [1], the width ofthe line is controllably varied so as to change the luminosity of theregions through which it passes. To increase the luminosity (orreflectance), the line is made narrower (i.e. less ink in the region).To decrease the luminosity, the line is made wider (i.e. more ink).

Whether the luminance in a given region should be increased or decreaseddepends on the particular watermarking algorithm used. Any algorithm canbe used, by changing the luminosity of regions 12 as the algorithm wouldotherwise change the luminance or colors of pixels in a pixelated image.

In an exemplary algorithm, the binary data is represented as a sequenceof −1s and 1s, instead of 0s and 1s. (The binary data can comprise asingle datum, but more typically comprises several. In an illustrativeembodiment, the data comprises 100 bits.)

Each element of the binary data sequence is then multiplied by acorresponding element of a pseudo-random number sequence, comprised of−1s and 1s, to yield an intermediate data signal. Each element of thisintermediate data signal is mapped to a corresponding sub-part of theimage, such as a region 12. The image in (and optionally around) thisregion is analyzed to determine its relative capability to concealembedded data, and a corresponding scale factor is produced. Exemplaryscale factors may range from 0 to 3. The scale factor for the region isthen multiplied by the element of the intermediate data signal mapped tothe region in order to yield a “tweak” value for the region. In theillustrated case, the resulting tweaks can range from −3 to 3. Theluminosity of the region is then adjusted in accordance with the tweakvalue. A tweak value of −3 may correspond to a −5% change in luminosity;−2 may correspond to −2% change; −1 may correspond to −1% change; 0 maycorrespond to no change; 1 may correspond to +1% change; 2 maycorrespond to +2% change, and 3 may correspond to +5% change. (Thisexample follows the basic techniques described in the Real Time Encoderembodiment disclosed in patent 5,710,834.)

In FIG. [1], the watermarking algorithm determined that the luminance ofregion A should be reduced by a certain percentage, while the luminanceof regions C and D should be increased by certain percentages.

In region A, the luminance is reduced by increasing the line width. Inregion D, the luminance is increased by reducing the line width;similarly in region C (but to a lesser extent).

No line passes through region B, so there is no opportunity to changethe region's luminance. This is not fatal to the method, however, sincethe watermarking algorithm redundantly encodes each bit of data insub-parts spaced throughout the line art image.

The changes to line widths in regions A and D of FIG. [1] areexaggerated for purposes of illustration. While the illustrated varianceis possible, most implementations will modulate the line width 3-50%(increase or decrease).

In still a further embodiment, the luminance in each region is changedwhile leaving the line unchanged. This can be effected by sprinklingtiny dots of ink in the otherwise-vacant parts of the region. In highquality printing, of the type used with banknotes, droplets on the orderof 3 μm in diameter can be deposited. (Still larger droplets are stillbeyond the perception threshold for most viewers.) Speckling a regionwith such droplets (either in a regular array, or random, or accordingto a desired profile such as Gaussian), can readily effect a 1% or sochange in luminosity. (Usually dark droplets are added to a region,effecting a decrease in luminosity. Increases in luminosity can beeffected by speckling with a light colored ink, or by forming lightvoids in line art otherwise present in a region.)

In a variant of the speckling technique, very thin mesh lines can beinserted in the artwork—again to slightly change the luminance of one ormore regions.

We have found that we can apply analogous and/or improved techniques tosteganographically encode specular reflective surfaces. With referenceto FIG. 2, a specular surface generally reflects light away from (andnot generally back to) the light's source. In one implementation, aspecular surface reflects light in a directional manner such that theangle of reflection is equal to the angle of incidence. While thespecular surface of FIG. 2 is illustrated as being adjacently arrangedwith a substrate, the present invention is not so limited.

Specular surfaces can be devoid of text or images, and often include ametallic-like surface luster (or finish). Examples of specularreflective materials include some of 3M's Radiant Light Films™ (e.g.,3M's Radiant Mirror and Visible Mirror products). The Radiant LightFilms™ can be combined with a Lexan® sheet (from GE Corporation) and anover-laminate (e.g., a polycarbonate, polyvinyl fluoride, polyester,etc.). Dorrie Corporation in the United States provides a variety ofsuitable laminates. Of course, a specular surface can include colorationand textures (e.g., tints, patterns, sparkles, etc.). Some of thesespecular surfaces even change color hue at different viewing angles andthinning ratios across the specular surface (e.g., 3M's Color MirrorFilm).

Steganographically encoding specular surfaces has heretofore presentedunique challenges. A first challenge is that with such a reflectivesurface, information is difficult to hide without being aestheticallydispleasing. A second challenge is signal detection. Some steganographicreaders include or cooperate with a light source (e.g., LED orillumination source) to facilitate better detection. Thesesteganographic readers often position or co-locate an optical sensor ator near the light source. Yet, with a specular surface, light reflectsaway from the light source (and optical sensor), yielding little or nooptical data for capture by the optical sensor. An optical sensor wouldneed to be placed along the angle of reflection to capture relevantoptical data. This configuration is awkward and practically impossiblefor a steganographic reader. Accordingly, it is very difficult tocapture and read a signal on a specular surface.

With reference to FIG. 3, we overcome these challenges by sprinkling (orproviding, over-printing, etc.) ink and/or dye on the specular surface.The ink or dye is provided on the specular surface so as to convey asteganographic signal.

The ink or dye is preferably selected or applied to blend in, hide orotherwise avoid contrast with the specular surface. For example, if thespecular surface includes a chrome, gold or silver coloration, the inkor dye preferably includes at least a complimentary chrome, gold orsilver coloration. Or if the specular surface includes a pattern orbackground, the ink or dye can be selected to match or otherwise blendin with the pattern or background. In other cases the ink or dye isgenerally opaque or transparent. Yet the transparent ink stillpreferably includes favorable reflective properties. Still further, theink can be selected to include a somewhat glossy finish so as to evenfurther improve the ink's hiding characteristics. In otherimplementations the ink includes a dull or even matt-like finish. A dullor matt-like finish may provide preferred reflection properties (e.g.,approximating Lambertian reflection) as discussed below.

The ink or dye preferably comprises a diffuse reflection surface orproperty. A diffuse reflection surface is one that generally diffuses alight ray in multiple directions, including, e.g., back toward thesource of the light ray (see FIG. 4 a). This characteristic allows forsteganographic signal capture by an optical sensor positioned at or neara light source. For example, the optical sensor captures optical scandata that includes a representation of the steganographic signal. Thecaptured scan data is communicated to a decoder to decipher thesteganographic signal. (In some implementations the ink approximatesLambertian reflection, which implies that the ink reflects light inmultiple directions, and hence can be perceived (or optically captured)from the multiple directions. With Lambertian reflection, the brightnessof a reflected ray depends on an angle between a direction of the lightsource and the surface normal.). We note, with reference to FIG. 4 b,that the optical sensor need not be positioned at the light source, butinstead can be positioned to receive another (or additional) reflectedlight ray(s). One FIG. 4 b implementation packages the optical sensorand light source in a signal apparatus (e.g., a hand-held steganographicsignal detector).

The steganographic signal preferably conveys a message or payload. Insome implementations the message or payload includes a unique identifierfor identifying the object or surface. Or the message or payload mayprovide authentication clues. In other implementations the message orpayload provides auxiliary information, e.g., pertaining to anassociated object or manufacturing details, distribution history, etc.In still other implementations the message or payload includes a link orindex to a data repository. The data repository includes the identifier,authentication clues, and/or auxiliary information. (See assignee's U.S.patent application Ser. No. 09/571,422, herein incorporated byreference, for some related linking techniques. The disclosed techniquesare suitably interchangeable with the linking aspect of the presentinvention.).

The steganographic signal may be optionally fragile, e.g., the signal isdestroyed (or irreproducible) or predictably degrades upon signalprocessing such as scanning and printing.

The steganographic signal may include an orientation component which isuseful in helping to resolve image distortion such as rotation, scaling,and translation, etc., and/or to help detect the message or payload. Theorientation component may be a separate signal, or may be combined (orconcatenated) with the message or payload.

The steganographic signal may also be redundantly provided across aspecular surface so as to redundantly convey the orientation, message orpayload (or plural-bit data). Or the signal may be object or locationspecific. For example, if the specular surface includes a graphic orbackground pattern/texture/tint, the signal can be limited to over thegraphic or background pattern/texture/tint.

In one implementation, the ink pattern is arranged according to aso-called digital watermark signal. The signal can be a “pure” or “raw”signal. A pure or raw digital watermark signal is generally one thatconveys information without influence or consideration of a host imageor text. In some implementations the pattern appears as (or includes) abackground texture or tint. In other implementations the pattern appearsas if a random (or pseudo-random) pattern.

In one digital watermarking implementation, and with reference to FIG. 5a, we start with a gray or monotone image (e.g., a flat gray imageincluding substantially uniform pixel values or subtly varying grayscaletexture, tint or pattern). We can use standard image editing softwaresuch as Adobe's Photoshop or Jasc Software's PaintShop Pro, etc., etc.to provide the gray image. The gray image serves as a “host” image andis passed to a digital watermark-embedding module (step 50). The digitalwatermarking module can encode the gray image, e.g., based on atransform domain watermark embedding technique or spatial domainwatermark embedding technique, etc. The resulting embedded, gray imageis then printed or otherwise applied to the specular surface (step 54).(In some implementations, a specular surface is provided as a thin film,which can be readily feed through an offset printing press or laser/inkjet printer.).

In another implementation, we “threshold” the embedded gray image priorto printing or applying to the specular surface (step 52 in FIG. 5 b).Generally, thresholding reduces the watermark signal and/or watermarkedimage. In one implementation, a watermark signal is embedded as aplurality of peaks and valleys (or plus and minus signal tweaks). Thetweaks can be encoded in a gray image by changing or effecting pixelvalues, e.g., changing gray-scale levels for pixels. (We note thattransform domain embedding also effects pixels values.). Thresholdingthis embedded gray image may then include selecting a grayscale level(e.g., level 128 in an 8-bit (or 256 level) grayscale image) anddiscarding all pixels with a grayscale level below (or above) level 128.Of course, there are many other thresholding techniques that can beemployed, such as filtering the embedded gray image, creating a binaryimage (e.g., toggling image pixels to be on or off based on pixel valuesof the embedded gray image), discarding pixels based on coefficientvalues (or blocks of coefficient values), etc., etc. The thresholded,embedded gray image is then applied or printed to the specular surface(56).

In some implementations two or more digital watermarks are provided inthe steganographic signal. The two or more watermarks can cooperate forauthentication. For example, each of the two watermarks may includeoverlapping payload information that can be compared to determineauthenticity. Or a first digital watermark may be fragile, while asecond digital watermark is robust. Still further, a first digitalwatermark may include an orientation component, while the second digitalwatermark includes a message or payload. Or a first digital watermarkmay include a key to decrypt or otherwise assist in decoding a seconddigital watermark.

If using a sheet of specular material (e.g., 3M's Radiant Light Films),ink can be printed (e.g., screen-printed, dye-diffusion thermal transfer(D2T2), and ink or laser jet printing, etc.) directly onto the sheet. Atie coat can be laid down on the film, prior to printing, to help theink better adhere to the film's surface.

The printed sheet can then be applied to an object such as a consumerdevice, electronics device, label, sticker, identification documents(e.g., driver's licenses, passports, identification cards, badges,access cards, etc.) certificate, automobile (e.g., as a paint substituteor as an overlay, etc.), credit cards, personal digital assistants(PDAs), molded logos (e.g., for attachment to articles such as shoes andclothing, equipment or consumer products), handheld and console videogames, pagers, dashboards, stereo faceplates or covers, plasticarticles, etc. The printed sheet can also be used as or in conjunctionwith a holographic structure or optical variable device. In some caseswe even use the specular surface as a hologram-like structure orcomponent.

In one embodiment, the printed sheet is provided to a molding process,e.g., as contemplated in our parent U.S. patent application Ser. No.10/286,357. In some implementations of this embodiment, the printedsheet is combined with (e.g., adhered to) a carrier sheet such as aLexan® polycarbonate sheet (Lexan® is provided by GE Plastics in theUnited States). A layered printed specular sheet/Lexan® sheet structureis also hereafter referred to as a “printed sheet.” The printed sheet isprovided to an injection mold, perhaps after pre-forming or pre-moldedthe printed sheet. The printed sheet is preferably positioned in themold so as to have the bottom surface of the printed sheet adjacent to asecond material, e.g., injected polycarbonate or polymeric resin (orother suitable injection materials). A three-dimensional object resultsincluding a printed specular sheet/Lexan®/injection material structure.(We note that the various layer materials will sometimes fuse or migrateinto other layers during an injection molding process.) We can alsoprovide an over-laminate (e.g., polycarbonate, polyester, polyurethane,etc.) over the printed specular surface. The printed steganographicsignal can be reversed if applied to a bottom layer of the printed sheetwhen the signal will be viewed from a top-surface of the printed sheet.Reversing the printing will typically allow for an easier read when thesignal is scanned from a top layer of the printed sheet.

In another molding implementation, we provide the printed specular sheetto be sandwiched in between a sheet of Lexan® and injection moldingmaterial. The Lexan® is preferably somewhat transparent to allow viewingof the printed specular surface through the Lexan®.

In a related embodiment, we provide a substrate (e.g., a Lexan® sheet)and a specular surface (e.g., a Radiant Light Film®) adjacently arrangedon or adhered to the substrate (collectively referred to as a“structure”). The specular surface is printed to include asteganographic signal as discussed herein. The structure can optionallyinclude a laminate layer. The structure is then used as a laminate orcovering. The laminate or covering is applied (e.g., with an adhesive orvia a molding process) to various objects (cell phones, automotiveparts, labels, identification documents, plastic parts, computerequipment, etc.).

Another embodiment involves the application of our techniques to compactdiscs (e.g., CDs, CD-Rs and CD-RWs) and digital video discs (e.g., DVDs,DVD-Rs and DVD-RWs). An example is given with respect to CD-Rs, but ourtechniques apply to other CDs and DVDs as well. With reference to FIG.6, a CD-R generally includes a multi-layered structure including aplastic (e.g., polycarbonate) substrate (61), a translucent data layerof recordable material such as an organic dye (62) and a specularreflective layer (63). Some CD-Rs also have an additional protective orprintable coating (64) adjacent to the specular reflective layer (63).

When making CD-R media, instead of pits and lands, a spiral is pressedor formed into the substrate, e.g., by injection molding from a stamper,as a guide to a recording laser. The recording laser selectively meltsthe translucent data layer of CD-R discs during the recording process.The positions where the data layer is melted becomes opaque orrefractive, scattering a reading laser beam so it is not reflected back(or is reflected as a different intensity) into a reader's sensors. Thereader interprets a difference between reflected and non-reflected lightas a binary signal.

We can apply our steganographic signal on a top or bottom side of thespecular reflective layer 63 (or other adjacently arranged layers) asdiscussed above. We preferably threshold the steganographic signal (orembedded grayscale image) prior to application to the specularreflective layer 63. A high threshold will help prevent reading errorsdue to the printed ink.

In one implementation of this embodiment, the steganographic signalincludes a decoding key. The decoding key is used to decode (or decrypt)the data (e.g., audio, video, data) on the disc. In anotherimplementation, the steganographic signal includes an identifier whichis used to determine whether the disc is authentic. Illegal copies willnot include the steganographic watermark on the specularsurface—evidencing an unauthorized copy.

Concluding Remarks

To provide a comprehensive disclosure without unduly lengthening thisspecification, each of the above-identified patent documents is hereinincorporated by reference.

Having described and illustrated the principles of the invention withreference to illustrative embodiments, it should be recognized that theinvention is not so limited. The present invention finds applicationbeyond such illustrative embodiments.

For example, the technology and solutions disclosed herein have made useof elements and techniques known from the cited documents. Otherelements and techniques can similarly be combined to yield furtherimplementations within the scope of the present invention. Thus, forexample, single-bit watermarking can be substituted for multi-bitwatermarking, technology described as using steganographic watermarks orencoding can alternatively be practiced using visible marks (glyphs,etc.) or other encoding, local scaling of watermark energy can beprovided to enhance watermark signal-to-noise ratio without increasinghuman perceptibility, various filtering operations can be employed toserve the functions explained in the prior art, watermarks can includesubliminal graticules to aid in image re-registration, encoding mayproceed at the granularity of a single pixel (or DCT coefficient), ormay similarly treat adjoining groups of pixels (or DCT coefficients),the encoding can be optimized to withstand expected forms of contentcorruption. Etc., etc., etc. Thus, the exemplary embodiments are onlyselected samples of the solutions available by combining the teachingsreferenced above. The other solutions necessarily are not exhaustivelydescribed herein, but are fairly within the understanding of an artisangiven the foregoing disclosure and familiarity with the cited art.

It should be realized that the reflectance characteristics shown inFIGS. 2, 4 a and 4 b are for illustrative purposes only. Of course, aspecular surface and applied ink can include additional or differentreflectance characteristics. Also, a specular surface is often providedas a thin film or sheet, which can be attached or adhered to a carriersheet or directly to an object surface. Hence, the FIGS. 2-4representations of a dome-like surface is only but one of the manypossible forms that a specular surface can take.

In an alternative embodiment, a specular surface includes a generallytransparent over-laminate (e.g., polycarbonate, polyurethane, and/orpolyester, etc.). The over-laminate provides protection to asteganographic signal printed or applied to the specular surface.

Also, instead of applying a steganographic signal on the specularsurface, we could provide a steganographic signal in or on a surface ofan over-laminate, yet this requires an additional layer.

In still another alternative embodiment, we print a thresholded digitalwatermark signal or other steganographic signal on an over-laminate orspecular surface using invisible (e.g., ultraviolet or infrared) inks.

In yet another embodiment, a thin film of specular material receives theprinted steganographic signal on a bottom or underside surface. The filmis sufficiently transparent so that the printed ink is viewable throughthe top surface of the film.

We note that some specular surface may be semi-specular. That is, theyreflect some light specularly and some light diffusely. Our inventivetechniques work well with such specular surfaces.

While specific dimension of sprinkled ink droplets are provided by wayof example in our parent application, the present invention is not solimited. Indeed, ink or dye can be arranged or printed onto a specularsurface using conventional printers and printing techniques. And dropletsize can be larger or smaller than given in the example.

The implementation of some of the functionality described above(including watermark or steganographic encoding and decoding) can beimplemented by suitable software, stored in memory for execution on anassociated processor or processing circuitry. In other implementations,the functionality can be achieved by dedicated hardware, or by acombination of hardware and software. Reprogrammable logic, includingFPGAs, can advantageously be employed in certain implementations.

In view of the wide variety of embodiments to which the principles andfeatures discussed above can be applied, it should be apparent that thedetailed embodiments are illustrative only and should not be taken aslimiting the scope of the invention. Rather, we claim as our inventionall such modifications as may come within the scope and spirit of thefollowing claims and equivalents thereof.

1. A mechanical part comprising: a metallic surface including a pattern,the pattern conveying plural-bit auxiliary data in a steganographicmanner, and the pattern provides at least diffuse reflection.
 2. Themechanical part of claim 1, wherein the pattern is provided on themetallic surface with an ink or dye.
 3. The mechanical part of claim 2wherein the metallic surface comprises a first color and the ink or dyecomprises a second color, the second color being chosen to help hide orconceal the ink or dye when provided over the first color.
 4. Themechanical part of claim 1 wherein the pattern conveying the auxiliarydata is provided with digital watermarking.
 5. The mechanical part ofclaim 4, wherein the auxiliary data is redundantly provided on themetallic surface.
 6. The mechanical part of claim 4, wherein the digitalwatermarking comprises a component to help resolve distortion introducedduring image capture.
 7. The mechanical part of claim 1, wherein thepattern is provided in the metallic surface with small indentations inthe surface.
 8. The mechanical part of claim 1 where the patterncomprises a dull finish.
 9. The an automotive part comprising themechanical part of claim
 1. 10. The mechanical part of claim 1, whereinthe diffuse reflection approximates Lambertian reflection.
 11. A methodcomprising: obtaining plural-bit auxiliary data; creating an originalcarrier signal representing the plural-bit auxiliary data; reducinginformation content of the original carrier signal so that the carrierstill conveys the plural-bit auxiliary data, yielding a reduced carriersignal; hiding the reduced carrier signal in host data.
 12. The methodof claim 11 wherein the act of hiding is accomplished with digitalwatermarking.
 13. The method of claim 11 wherein the host data resideson a mechanical part.
 14. The method of claim 11 wherein the host datacomprises audio or video.
 15. A computer readable medium comprisinginstructions or circuitry to perform the method of claim
 11. 16. Amechanical part comprising: a shiny or metallic surface including apattern, the patter including or representing the auxiliary data in asteganographic manner, the pattern providing diffuse or Lambertianreflection.
 17. The mechanical part of claim 16 wherein the pattern isprovided with an ink or dye and wherein at least one of a coloration orfinish of the ink or dye is selected to hide the ink or dye with respectto at least one of a first coloration or the first finish.
 18. Themechanical part of claim 16, wherein the pattern is provided in theshiny or metallic surface through small indentations in the surface.